Flotation of acidic minerals



Feb. 13, 1945. H' MEAD ET'AL 2,369,311

FLOTATION OF ACIDIC MINERALS 4 i Filed oct. 12, `194,2

l l l I I l I VP/V557 a. M4 as r,

ATTORNEY Y beneflciation of Patented Feb. 13, 1945 Harry L. Mead and Ernest J. Maust, Fla., assignors to American Brewster, Cyanamld Company, New York, N. Y., a corporation of Maine Application October 12, 1942, Serial No. 461,766

` (ci. s-1st) t froth flotation, whereby the acidic gangue is con- 3 Claims.

This invention relates tothe concentration of minerals by froth flotation, more particularly to the beneficiation of ores by floating acidic gangue therefrom.

Beneciation of ores by froth flotation, using a cationic-type reagent to float one or more cornponents from the residue has become a well known procedure. In some cases, an operation of this type has a definite advantage over the use of an anionic-type reagent to float the mineral values away from the gangue. This-is particularly true in those cases Where the anionic reagents suitable for use with the mineral to be concentrated are not sufllciently selective. In such cases, although good recoveries can be made, it is diillcult to produce a concentrate of high grade. This difficulty very commonly appears, for example, in the benelciation of non-sulde ores containing silica-bearing gangue such as silica, or silicates such as mica and the like minerals.

Phosphate ores, such phate, are typical of A are readily adapted to beneciation with these reagents. Accordingly, that ore will be used as illustrative in setting forth the process of the present invention. The invention, however, is not so limited. It may be equally Well applied to the any ore Yin which an acidic gangue from the mineral values. Among can be treated according to the as Florida pebble phosis to be floated the ores which process of the present invention are those in A which the acidic mineral is to be separated from ores suchas limestone, bauxite, barytes, ilmenite, calcite and the like.' 'I'he process is equally applicable whether the acidic mineral is being concentrated as sangue or as product.

'I'he invention will be more fully illustrated in connection with the following drawing which is 'thought to be substantially self-explanatory and in which:

Figure 1 represents a flow sheet of process of the prior art; and,

Figure 2 represents a flow-sheet showing the modified procedure of the present invention.

The use of cationic-type reagents in concentrating acidic gangue is not new per se, being well illustrated for example in U. S. Patent No. 2,205,503. Theactual practice of such a process is relatively simple. In its general form, such practice is diagrammatically set forth in the flow scheme of Figure 1. As shown in Figure 1, the ore to be beneflciated is ground, deslimed to the necessary degree, pulped with water, thepulp conditioned with the reagent and then subjected to a typical the non-suliide ores which centrated and collected.` The froth concentrate is usually passed to a second machine and given t a cleaner flotation without the use of additional reagents, although such reagents may be added if necessary. The middlings from this cleaner float are ordinarily small inquantity and can be either discarded or optionally recycled to the rougher flotation according to their mineral content.

As a process, this beneficiation procedure appears to be both simple and effective. Actually, it suffers from anum-ber of practical drawbacks. First, the reagent cost, on the lbasis of the weight of ore being treated, as compared with that for anionic-type reagents is high. The principal advantage of cationic reagents lies intheir ability to produce a higher grade Vproduct having an increased net value despite the increased reagent cost. This advantage canvbe obtained only when the cationic flotation is carefully controlled to take the fullest possible advantage of the concentrating power of the cationic reagent.

Secondly, cationic-type reagents are` not perfectly selective. In other words, cationic reagents, like the anionic-type, can not be depended upon to make an exact separation of the desirable and the undesirable materials. 'Ihis fact presents a particularly serious drawback in the case of cationic-type reagents.- Not only is there a direct loss of potential productgbut so much of the reagent as is used in floating this potential product is also Wasted so far as performing use- Vful work is concerned. These combined effects may so increase the net cost of producing a highengrade product, that any economic advantage therefrom is lost.y The'losses may in some cases be great enough Vto place the cationic reagentat a disadvantage.

In the use of these cationic reagents, the pres` ence of shines is also very troublesome. For example, in the beneficlation of phosphate ores the presence of even a small fraction of one percent of slimes in the feed may increase the reagent consumption to a point at which the operation is economically undesirable. In many cases, the presence of excessive shines may render the process inoperative. be very thoroughly deslimed. This adds to the cost of the operation and increases the necessity for obtaining the maximum benefit of the reagents concentrating power.

In those operations, such as the benelciation of phosphate ore, in which the unit profit is small these considerations are specially impor- As a consequence, the feed mustV tant. The premium for high grade is relatively important as compared with the base price. A change in thenet value of the product of even a 'ew cents per ton may make the difference between a process which is commercially desirable and one which is not. Any loss in potential concentrating power` of the reagents is aggravated by the tremendous production rate of an even tional improvement in grade is made at the expense of increased' losses in product which in turn offset the economic advantages of producing a higher grade.

As a result, the cationic reagent is usually used in such a way that neither the maximum improvement in grade nor the maximum potential recovery is obtained. vIn the case of phosphate ores, for example, the demand for high grade product places the emphasis on grade rather than recovery. As a result considerable phosphate is lost by being carried oif in the silica rougher concentrate. Part of this potentially salable product is recovered by retreating -the middlings. Nevertheless, an appreciable quantity of salable product'which it is highly desirable to recover is 10st in the silica cleaner concentrate.

It is, therefore, an object of the present invention toestablish a procedure by which a maximum utilization of the concentrating power of the reagent and a maximum recovery of salable product are more nearly realized. The present invention is particularly concerned with obtaining the maximum recovery of useful product, without a sacrifice in grade.

Surprisingly enough, the object of the present invention is accomplished by going contra to established practice. as shown in Figure 1, is to a'dd all the feed during the rougher flotation and sebsequently clean the silica concentrate. According to the present invention, as shown in Figure 2, instead of feeding all the material to the rougher flotation machine, an appreciable .quantity is added to the cleaner circuit. This greatly increases the physical quantity of middlings which are then utilized as a part of the feed to/ the rougher flotation.

Also, as shown in Figure 2, instead of basing the amount of reagent on the usual economic balance, the process contravenes the usual practice by using an excess of reagent to carry out the rougher concentration. As a result of combining what the art has taught to be a Waste of reagent with what has been considered a reversal of the necessary feeding procedure, the amount of potentially useful product in the cleaner concentrate may be greatly reduced. Losses of product are reduced by as much as .B5-50% below those obtainable by the best conventional practice.

Although the present invention is not intended to be limited by any particular theory of operation it is believed that the improved result is due to a combination of several factors. First, a considerable amount of excess reagent, over that which is used in the conventional practice, is employed in the rougher flotation, This enables the production of an excellent gangue COI!- to increase the removal The present practice, as

centration. However, as a result, the froth concentrate also contains a considerable quantity of unused reagent. Instead of losing any reagent removed in the froth, as in the prior practice, it is quickly utilized in floating a part of the easily floatable gangue from the fresh feed added during the cleaner notation.

In addition, an appreciable amount of reagent is used up by reacting with the basic mineral, whereby the charge on a part of the product mineral is neutralized or reversed and these product particles are floated out in the froth concentrate. However, the reagent normally has a greater affinity for an acidic gangue than for the product. Accordingly, when this abnormally charged portion of the product is brought into contact with the large amount of easily floatable gangue in the fresh feed during the cleaner flotation, it undergoes another charge transference. The reagent leaves the abnormally charged particles and is utilized in floating additional gangue. The now normally charged product particlesv settle out in the middlings and are recovered. Product losses in the cleaner concentrate are thereby reduced.

In addition to these direct recoveries, another factor adds to the overall efficiency of the entire process. As was noted above, because a part of the feed is added to during the cleaner flotation,

the amount of middlings is increased. Adding these middlings to the rougher flotation results ,in an amount of material equal to this increase being subjected to flotation for longer than the normal length of time. Because of this increased time, the rougher flotation can produce an even better separation.

In addition, a further advantage is obtained because a part of the gangue content has already been removed before the total feed reaches the rougher flotation stage. Consequently, a greater quantity of yfeed may be treated for an equal amount of gangue to be removed, This enables a greater total through-put for a fixed amount of equipment and results in a greater overall efficiency.

Expressed in other terms, this advantage of the process of the present invention means that a greater amount of gangue may be concentrated with a fixed amount of reagent. For exam.- ple, in beneiiciating phosphate ore, using a xed amount of reagent, as much astwenty percent or more of gangue can be concentrated.

The term cationic reagents as used in the present specification and claims is intended to include the general class of such compounds having large, positively charged surface-active ions, many of which have become known as promoters for the flotation of acidic gangue. These positively-charged ions are usually of relatively large'size and weight and usually contain at least one amine, ammonium or other onium" group.

Examples, for illustrative purposes only, of the commonly used. reagents of this type include amines such as the lauryl or octadecyl amines andthe like. Similarly, use has been made of the readily ionized amine salts such as the hydrochloride, acetate and the like. Other examples include, for example, quaternary compounds such as cetyl pyridinium bromide or chloride, lauryl trimethyl ammonium chloride or iodide and the like. lStill another well known type includes compounds, such compounds as the polyalkylene polyamines, their condensation products with fatty acidsand the ilts thereof.

'I'vhe process of the'present invention can not y were pulped with 2300 parts of Water.

be readily limited as to the proportion of the total feed which should be added to the circuit inthe cleaner stage. 'I'he amount` required will obviously vary with circumstances, being dependent not only upon the nature and conditions of the ore but also upon the particular reagent being used. The critical factor appears to be the proportion of the gangue in the feed which, principally due to its size, is easily oatable. For the optimum results it is necessary to add enough fresh feed to the cleaner stage so that a suilicient amount of this easily oatable portion of the gangue will be available to use up the excess reagent and effect the charge transference. This will again obviously vary with circumstances, being particularly affected by changes in the nature of the ore, the eiliciency of the grinding, the extent of desliming and'other pre-treating processes.

Fortunately, however', the process is not critical as t the upper limit of the amount of material which may be added. A considerable excess of material over and ,above that necessary for the optimum result, may be present without adversely affecting the entire process. This can be taken advantage of by adding more than enough feed in the cleaner stage so that there will be present at all times enough easily iloatable gangue to take care of the exceptional circumstances. In fact, as pointed out above, there is a certain advantage in adding as much feed at this point as can final grade. Addition of fresh feed in this way increases the total overall recovery at a rate faster than the corresponding decrease in grade over a considerable range.

While the above discussion has been largely limited to phosphate benecation from ores containing a siliceous gangue, this was only because such ores are typical of the types which can'be advantageously treated according Ate the process of the present invention. Because they are typical, phosphate ores will be used to illustrate the 4invention in the following examples in which all parts are by weight unless otherwise noted.

EXAMPLE 1 As illustrated of the prior art procedures 500 parts of a Florida pebble phosphate ore, assaying 31.63% B. P. L., -which had been previously deslimed, polished and very thoroughly deslimed 0.72 lb./t. of a mixed polyethylene polyamine flotation reagent were added as a 2% solution, the mixture was passed to a Fagergren fiotation machine, conditioned for 3 seconds and the silica concen trate removed. The silica concentrate was passed t0 a second Fagergren flotation machine, agitated for one second and the silicate cleaner concentrate removed.- The results are shown in Table I.

TabZeI Phosphate railing Middling Silica conm' Phostrate phate 1 overall Percent Percent Percent s Percent 'recovery' 13. P.L insti. Wt- B. P. L. t B. P.,Lf.' WL Percent 78.20 .s0 100 02.00 1s 4.43 31a 01.0

ExAMPLE2 The procedureofExample l was repeated but 174 parts of fresh feed were added in the cleaner be done without effecting the parts or 22.8% more than was obtained in EX- circuit. parts of middlings were obtained. 'The results are shown in Table II.

. l Table II im L S ica concenl Phosphate telling Mlddling trate Phosphate overall Percent Percent Percent Percent recovery' B insel. Wt- B.P.L. L n. P. L. WL percent It will be noted that in this test a total of 372 parts of silica concentrate was floated, this being i 39 parts or 18.8% ample 1, using t both cases.

more than was oated in Exe same amount of reagent in EXAMPLE 3 The procedurerof Example 2 was repeated, adding 264 parts of feed to the cleaner otation. 'I'he results are shown in Table III.

With the additional amount of feed added to the cleaner cell in this test, a total of 374 parts of silica concentrate was floated,representing 61 parts or'19.4% more that iloated in Example 1 using identical amounts of reagent. i

EXAMPLE 4 The procedure of Example 1 was repeated substituting 0.28 lb./t. of Armour amine hydrochloride (approximately Cia) fed as an emulsion com.. prising 1.5 parts of the amine hydrochloride, 2 parts of a higher aliphatic alcohol frother (approximately C'i-Ce) and 72 parts of water. No

feed 'was added in the cleaning circuit. The results are shown in Table IV.

Table IV Phosphaiemiling Middiing Silicrgtgn' Plilms p ate overall Percent Percent Percent Percent recovery B.P.L insti. Wt' B. P. L. Wt B. P. L. WL Percent EXAMPLE 5 Example 4 was repeated adding 180 parts of feed in the cleaner stage. 'I'he results are shown in Table V.

Table V Phosphate failing Middiing Scrggn' giga; overall Percent Percent Percent Percent recovery B.P.L insti. Wt- B. P. L. Wt B. P. L. WL percent It is also to be noted in this test that 371 parts of silica concentrate was obtained, this being 69 ample 4, using both cases.

We claim:

1. In those processes of beneficiating ores by froth flotation in which an acidic mineral is floated from a non-acidic mineral by the aid of a cationic-type promoter the improvements which comprise the steps of dividing the feed into a major and a minor fraction; subjecting the major portion of the feed to a rougher flotation in the presence of a 'sufficient excess of promoter to insure an underfiow sufficiently low in acidic mineral content, whereby the excess promoter and a normally excessive amount of non-acidic mineral are carried oif in the overflow; subjecting the rougher flotation overflow to a cleaner flotation together with the minor fraction of the feed, said minor fraction of the feed being sufficient toinsure the utilization of the excess promoter and the settling of substantially all of the non-acidic mineral content of the rougher flotation overflow, and returning the underflow from the cleaner otation to the rougher flotation circuit.

2.In those processes of beneciating ores by `froth flotation in which the gangue is floated away from the mineral by the aid of a cationictype promoter the improvements which comprise dividing the feed into a major and a, minor fraction, subjecting the major fraction to a rougher flotation in the presence of a sufficient amount of a cationic-type promoter to insure an underflow sufficiently low in gangue, whereby a normally excessive amount of mineral and the excess promoter is carried off in the rougher flotation overflow, subjecting the rougher flotation overflow together with the minor fraction of the feed to a cleaner flotation, said minor fraction of feed being sufficient to insure the utilization of the excess promoter and the settling of substantially all the mineral in the rougher flotation overow, and

returning the cleaner flotation underfiow to the rougher flotation feed.

3. In those vprocesses of beneficiating phosphate ores by froth flotation in which the silicabearing gangue is floated away from the mineral by the aid of a cationic-type promoter the improvements which comprise dividing the feed into a major and a minor fraction, subjecting the majorfraction to a. rougher flotation in the presence of a sufficient amount of a cationic-type promoter to insure an underflow suiiiciently low in silicabearing gangue,`whereby a normally excessive amount of mineral and the excess promoter is carried off in the rougher flotation overow, subjecting the rougher flotation overflow together with the minor fraction of the feed to a cleaner flotation, said minor fraction of feed being sufcient to insure the utilization of the excess promoter and the settling of substantially al1 the mineral in the rougher flotation overow, and

returning the cleaner flotation underflow to the rougher iiotation feed.

HARRY L. MEAD.

ERNEST, J. MAUST. 

